Fire detection systems for the protection of personnel and property have spawned an entire industry dedicated to the manufacture, sale and installation of systems that provide early warning of the existence of combustion. The most common of these is, of course, the smoke detector, that relies on some sort of optical or ion detector to indicate the presence of smoke. Other systems, such as sprinklers, utilize the heat of combustion to trigger a warning and to inundate an area with a fire-extinguishing medium.
While such systems are highly useful and protective of personnel and property, they serve only to detect combustion after it has occurred. Consequently, a number of systems have been designed and built to detect incipient combustion. One such system designed and operated by Fermi National Laboratory, relies on an early warning system based on an evolved gas signature. Incipient detection systems of this type tend to be site specific due to their mode of operation. Such systems generally operate according to the following steps: 1) an analysis of likely ignition (combustion) scenarios and of the combustible fuels in a given area is performed; 2) the most likely fuel or combination of fuels to initiate combustion is determined; 3) a literature search is performed to determine what gases are given off by this material or combination of materials when heated; 4) detectors for these gases are obtained and either located in the area of interest for protection or connected to a gas sampling system capable of delivering the objective gas to the detector; and 5) upon detection of a predetermined concentration level of the objective/analyte gas an alarm is indicated. While such systems are entirely satisfactory for certain environments, they tend to be site specific, i.e. dependent upon the contents of the particular area of concern, and their installation tends to be time consuming and virtually a separate research project as all combustibles in the area must be characterized, their relative combustibility determined and suitable detection means and apparatus obtained and installed. Also, the introduction, intentionally or otherwise of an "uncharacterized" fuel(s) may negate the value of the entire system.
Yet another method used to detect incipient combustion involves the use of simple temperature detection devices. In such systems, simple thermometric devices or more sophisticated IR temperature sensors are placed proximate the potential source or sources of combustion and upon the attainment of a predetermined temperature an alarm or warning is instituted. Again, these systems are very useful and entirely appropriate for certain applications, however, they are generally not capable of providing coverage of large areas since the thermometer or other temperature sensing device must be located or "focused" in or on a particular small area where combustion is anticipated to occur. Such temperature sensing systems that monitor relatively large areas, are generally not capable of detecting a suitable, detectable temperature rise until after combustion has been initiated. Similarly, while such simple temperature detection systems based upon thermometric devices of one sort or another are capable of detecting the temperature rise of an entire area, they are not well suited to detecting potential temperature rises in a large number of small potential heat sources without the installation of numerous temperature detecting devices.